// Modified from https://github.com/egoist/markdown-it-highlight-lines
import type MarkdownIt from 'markdown-it';

const RE = /{([\d,-]+)}/;
const wrapperRE = /^<pre .*?><code>/;

export const highlightLinePlugin = (md: MarkdownIt) => {
  const fence = md.renderer.rules.fence!;
  md.renderer.rules.fence = (...args) => {
    const [tokens, idx, options] = args;
    const token = tokens[idx];

    const rawInfo = token.info;
    if (!rawInfo || !RE.test(rawInfo)) {
      return fence(...args);
    }

    const langName = rawInfo.replace(RE, '')?.trim();
    // ensure the next plugin get the correct lang.
    token.info = langName;

    const lineNumbers = RE.exec(rawInfo)![1]
      .split(',')
      .map(v => v.split('-').map(v => parseInt(v, 10)));

    const code = options.highlight ? options.highlight(token.content, langName) : token.content;

    const rawCode = code.replace(wrapperRE, '');
    const highlightLinesCode = rawCode
      .split('\n')
      .map((_split, index) => {
        const lineNumber = index + 1;
        const inRange = lineNumbers.some(([start, end]) => {
          if (start && end) {
            return lineNumber >= start && lineNumber <= end;
          }
          return lineNumber === start;
        });
        if (inRange) {
          return `<div class="highlighted">&nbsp;</div>`;
        }
        return '<br>';
      })
      .join('');

    const highlightLinesWrapperCode = `<div class="highlight-lines">${highlightLinesCode}</div>`;

    return highlightLinesWrapperCode + code;
  };
};
